Disk file suspension assemblies suspend a slider in close proximity to a moving disk in order that a transducer on the slider may read and/or write data on the disk. The function of the suspension assembly is to maintain the correct attitude of the slider for operation with the disk drive.
Disk drive suspension assemblies typically include, as component elements, a base plate or other mount platform, a load beam, a gimbal flexure and the slider. The load beam is an elongated metal spring structure The base plate is attached to a proximal end of the load beam, and is configured for mounting to an actuator arm of a disk drive. In some instances, the load beam is directly attached to the actuator arm The gimbal flexure is positioned on the distal end of the load beam The slider is mounted to the gimbal flexure and is supported thereby in read/write orientation with respect to an associated disk.
The suspension loads the slider into position against the disk, and the rotation of the disk creates an air stream which generates an air bearing between the disk and the slider, lifting the slider away from the surface of the disk. The resultant air bearing supports the slider nanometers away from the surface of the disk. The gimbal flexure provides gimballing support, that is, the gimbal flexure positions and maintains the slider at a desired air bearing "flying" attitude, a predetermined angle and height in relationship to the disk surface.
The static attitude of the slider, the position of the slider at rest with respect to the mount platform, is calibrated so that the slider can maintain an optimal flying height for the transducer thereon to read and/or write data onto the recording surface of the disk.
To counter the air lift pressure exerted on the slider during disk drive operation, a predetermined load is applied through a load point on the suspension to a precise load point on the slider. The slider flies above the disk at a height established by the equilibrium of the load on the load point and the lift force of the air bearing. The load of the suspension, together with the static attitudes, control and maintain the optimal flying height of the slider.
A conventional gimbal flexure, sometimes referred to as a Watrous gimballing flexure design, is formed from a single sheet of material and includes a pair of outer flexible legs about a central aperture and a cross piece extending across and connecting the legs. A flexure tongue is joined to the cross piece and extends from the cross piece into the aperture A free end of the tongue is centrally located between the flexible legs. The slider is mounted to the free end of the flexure tongue.
The free end of the flexure tongue positions the slider so that the load point of the slider is directly over the load point of the load beam The slider is then free to pivot about the load point as allowed by the gimbal structure. Any deviations caused by a lack of precision or distortion in forming or assembling the individual elements of a suspension contributes to a variation in static pitch and roll attitudes of the slider. The result of these static attitude variations is static pitch and roll torque which affect the desired flying height of the slider.
Static roll torque and static pitch torque have their rotational axes at about the center of the slider in perpendicular planar directions, and are caused by forces acting on the slider due to the air bearing surface not being parallel to the disk surface while the slider is flying over the disk. That is, static torque is the rotational force tending to rotate the slider out of parallelism with the disk surface while the slider is flying over the disk.
The ideal or desired pitch and roll attitudes are best defined as those which would not result in any pitch and roll torques when the suspension is installed in a disk drive. In an actual disk drive, pitch and roll static torques produce adverse forces between the air bearing surface of the slider and the disk, affecting the attitude of the slider and therefore the flying height of the slider above the disk, resulting in deviations from optimum read/write transducer/disk interface separation.
In the static attitude forming a conventional flexure design, the flexure legs and tongue are formed offset from a first section of the flexure toward the slider. The offset is formed where the flexure legs join the first section, or, in another example, where the flexure tongue and the cross piece join. The standard flexure design evidences a low value of pitch stiffness and moderate value of roll stiffness.
The flexure design is made so as to achieve a precise method of fabrication that accurately compensates and corrects for manufacturing variations that currently contribute to static pitch and roll torque errors. Since the roll torque axis is along the longitudinal axis of the flexure, roll torque errors are easily correctable.
The more difficult correction in the manufacturing process is the ability to perform corrections for pitch static attitude (PSA), since the corrections have to be made along the axis perpendicular to the longitudinal axis of the flexure. The ability to correct for the pitch static attitude is critical for proper flexure/slider/disk alignment in order to achieve a tight flight height tolerance. Any pitch misalignment of the slider will adversely affect the air bearing relationship of the slider to the disk and therefore adversely affect the flight height of the slider and transducer.
However, the PSA is changed during the assembly process. The first change is induced by dimple interference during the flexure and load beam assembly process. The dimple may be provided in the load beam and protrude from the load beam toward the flexure tongue, or the dimple may be provided in the flexure tongue and protrude from the tongue toward the load beam The dimple is normally made with a height at least equal to the flexure offset. Thus, when the load beam and the flexure are assembled, the dimple interference fit will force the tongue away from the load beam at an angle from the plane parallel to that of the load beam and of the first section of the flexure. The arm or base plate, load beam and flexure are then welded together and are likely to undergo another PSA change during this process.
For a laminated "integrated lead suspension assembly" (ILS), where the leads are formed by etching a conductor layer on a dielectric layer to form conductor traces, the PSA will change again during the head termination process which may comprise a bending of the leads into contact with a side of the slider for ultrasonic bonding to the transducer on the slider, may comprise solder or gold balls which are placed on the leads while supported by the dielectric and steel layers and heated to make contact between the leads and the transducer, or may comprise other methods.
The integrated lead suspension assembly has integrated copper traces acting as conductive wires. Although more predictable than the earlier individually assembled wires, the copper traces are stronger than the conventional wires. In the ultrasonic bonding example, these etched copper leads at the gimbal area are formed into a hook shape, which is called a bent lead, for use with the ultrasonic bonding process for slider/transducer termination. In reality, the distance from the bent lead to the corresponding slider termination pad has a relatively large tolerance Due to the strength of the bent lead, there will be a residual moment resulting from distortion of the flexure during termination which has to be balanced between the slider and bent lead platform after slider/transducer termination. This residual moment will drive the PSA change.
For the integrated lead suspension assembly using other termination approaches, such as solder or gold ball termination, the PSA change is caused by another mechanism. In this case, the flexure tongue and steel layer of the suspension will be in the same level before the slider/transducer is terminated to the trace conductors. The trace conductors will be etched back from the dielectric layer so that the dielectric will extend toward the slider beyond the edge of the conductor to prevent a potential short The dielectric layer will therefore be pushed down by the thickness distance of the dielectric under the slider during slider bond and the PSA will change. The magnitude of the PSA change depends on the coupling strength of the slider to the flexure tongue and the thickness of the dielectric.
The adjustment of the PSA is required in the manufacturing process to reduce the PSA to an acceptable range. The problem is that the adjustment at the conventional points of offset are so far removed from the slider that the PSA adjustable range is very limited. It is very difficult to adjust in a wide range. The other PSA adjustment through the load beam will affect the overall dynamic performance which is not preferred.
Thus, what is needed is a flexure assembly that may be precisely adjusted with a wide PSA adjustable range and insensitive to PSA change during slider bonding and transducer termination so as to achieve high quality and high yield.